Building your own stereo tube amplifier is a great way of creating a versatile piece of musical equipment. Stereo tube amplifiers are great for creating modulated and spacey guitar sounds. The stereo configuration of two speakers enables you to shift the signal phase between the pair. The signal processing part of your amplifier will duplicate and delay the signal, so the speakers are out of phase. You can build your stereo tube amplifier based on the specifications of a commercially made amp that you like, or you can use your own spec.
Acquire your parts. The easiest way to get the necessary components is to purchase a stereo tube amplifier kit. For example, the "Classic Guitar Amps" website has a kit that emulates the four speaker Fender Bassman amp. You need at least two speakers to achieve stereo. You can salvage your parts from an old or damaged amplifier, such as a Fender Twin. This amp is a classic tube-powered stereo combo.
Measure the speakers and mark out on the cabinet's support struts where to screw them in. If the cabinet isn't preassembled this will be easier. If it is preassembled you'll need to reach inside the cab to make the measurements.
Prepare your cabinet. Depending on the kit model, this will come either preassembled, part-assembled or completely assembled. Follow the assembly instructions that come with the kit to fit it together. Use a strong polyvinyl acetate to fit the corners of the side and top panels together. Screw them together once the glue has dried. Slot the amp chassis shelf into the cabinet. If you are salvaging your parts the cab will be prebuilt.
Fit the speakers. Screw them into the holes that you marked on the support strut.
Assemble the circuit board. The circuit board processes and manipulates the audio signal. Solder the surface-mounted components in place as per the schematic and assembly instructions.
Fit the circuit board to the chassis. The amp chassis contains the preamp and power amp sections. The preamp converts the input signal into an electrical current. The circuit board controls the flow of the signal once it reaches the preamp. Solder the input jack terminal to the input terminal of the printed circuit board. The potentiometers dictate the flow of current. Each time you turn a dial on the amp, the potentiometer increases or decreases the current sent to the circuit board. Solder each potentiometer to the relevant place on the board, as per the wiring schematic.
Power the speakers. The power amp adds a voltage to the audio signal's electrical current, which it then sends to the speakers. Solder two wires to the output terminal on the power amp and slot them through the hole marked on the wiring diagram.
Fit the chassis lid. Depending on the kit model, this is either screwed or soldered on. Slot the fully assembled chassis into the shelf. Take the wires that you connected to the output terminal on the power amp and solder one to each speaker.
Load the tubes into the tube bases on the exterior of the amp chassis. Fit the front grille and screw on the back panel.
Wear surgical gloves when fitting the tubes. Oils from your skin can create hot spots on the glass.
If you are unsure at any stage during your amp project, consult a professional. Amplifiers can carry a potentially lethal current.
Tips and warnings
- Wear surgical gloves when fitting the tubes. Oils from your skin can create hot spots on the glass.
- If you are unsure at any stage during your amp project, consult a professional. Amplifiers can carry a potentially lethal current.